1. Field
Embodiments disclosed herein relate generally to solid state processing of materials through friction stirring, which includes friction stir processing, friction stir mixing, and friction stir welding. This invention also relates to the application of the friction stir processes to the manufacturing of roller cone drill bits used in wellbore operations, oil field and mining equipment and tools, and components or parts used in other industrial and medical applications. In particular, embodiments disclosed herein relate generally to ball hole plugs and methods of welding ball hole plugs to roller cone drill bits using friction stir welding.
2. Background Art
Friction stir welding (hereinafter “FSW”) is a technology that has been developed for welding metals and metal alloys. The FSW process often involves engaging the material of two adjoining workpieces on either side of a joint by a rotating stir pin or spindle. Force is exerted to urge the spindle and the workpieces together and frictional heating caused by interaction between the spindle and the workpieces results in plasticization of the material on either side of the joint. The spindle is traversed along the joint, plasticizing material as it advances, and the plasticized material left in the wake of the advancing spindle cools to form a weld.
FIG. 1 is a perspective view of a tool being used for friction stir welding that is characterized by a generally cylindrical tool 10 having a shoulder 12 and a pin 14 extending outward from the shoulder. The pin 14 is rotated against a workpiece 16 until sufficient heat is generated, at which point the pin of the tool is plunged into the plasticized workpiece material. The workpiece 16 is often two sheets or plates of material that are butted together at a joint line 18 but could also be cylindrical or other non-flat materials or surfaces. The pin 14 is plunged into the workpiece 16 at the joint line 18.
The frictional heat caused by rotational motion of the pin 14 against the workpiece material 16 causes the workpiece material to soften, preferably without reaching a melting point of the workpiece material. The tool 10 is moved transversely along the joint line 18, thereby creating a weld as the plasticized material flows around the pin from a leading edge to a trailing edge. The result is a solid phase bond 20 at the joint line 18 that may be generally indistinguishable from the workpiece material 16 itself, in comparison to other welds. However, it has been discovered that the solid phase bond 20 may be created to also have different and advantageous properties as compared to the original workpiece material 16.
It is observed that when the shoulder 12 contacts the surface of the workpieces, its rotation creates additional frictional heat that plasticizes a larger cylindrical column of material around the inserted pin 14. The shoulder 12 provides a forging force that contains and/or forces downward the generally upward metal flow caused by the tool pin 14.
During FSW, the area to be welded and the tool are moved relative to each other such that the tool traverses a desired length of the weld joint. The rotating FSW tool provides a continual hot working action, plasticizing metal within a narrow zone as it moves transversely along the base metal, while transporting metal from the leading face of the pin to its trailing edge. As the weld zone cools, there is typically no solidification as no liquid is created as the tool passes. It is often the case, but not always, that the resulting weld is a defect-free, recrystallized, fine grain microstructure formed in the area of the weld.
Travel speeds of the pin 14 along the joint line 18 are typically around 10 to 500 mm/min with rotation rates of 200 to 2000 rpm. However, operating parameters outside of this range may also be used. Temperatures reached in FSW are usually close to, but below, solidus temperatures of the base materials. Friction stir welding parameters are a function of a material's thermal properties, high temperature flow stress and penetration depth.
Friction stir welding has several advantages over fusion welding because 1) filler metal is not required, 2) the process can be fully automated requiring a relatively low operator skill level, 3) the energy input is efficient as all heating occurs at the tool/workpiece interface, 4) minimum post-weld inspection is required due to the solid state nature and extreme repeatability of FSW, 5) FSW is tolerant to interface gaps and as such little pre-weld preparation is required, 6) there is no weld spatter to remove, 7) the post-weld surface finish can be exceptionally smooth with little to no flash, 8) there is little or no porosity and oxygen contamination, 9) there is little or no distortion or surrounding material, 10) minimal operator protection is required as there are no harmful emissions, and 11) weld properties are improved.
Previous patent documents have taught the benefits of being able to perform friction stir welding with materials that were previously considered to be functionally unweldable. Some of these materials are non-fusion weldable, or just difficult to weld at all. These materials include, for example, metal matrix composites, ferrous alloys such as steel and stainless steel, and non-ferrous materials. Another class of materials that were also able to take advantage of friction stir welding is the superalloys. Superalloys can be materials having a higher melting temperature than bronze or aluminum, and may have other elements mixed in as well. Some examples of superalloys are nickel, iron-nickel, and cobalt-based alloys generally suitable for use at temperatures above 1000 degrees F. Additional elements commonly found in superalloys include, but are not limited to, chromium, molybdenum, tungsten, aluminum, titanium, niobium, tantalum, and rhenium.
It is noted that titanium is also a desirable material to friction stir weld. Titanium is a non-ferrous material, but has a higher melting point than other nonferrous materials.
Those skilled in the art have previously taught that a tool is needed that is formed using a material that has a higher melting temperature than the material being friction stir welded. In some embodiments, a superabrasive was used in the tool.
The embodiments of the present invention are generally concerned with these functionally unweldable materials, as well as the superalloys, and are hereinafter referred to as “high melting temperature” materials throughout this document. It is noted that the principles of the present invention are also equally applicable to materials that are considered lower melting temperature or functionally weldable materials.
In line with friction stir welding, the inventors have determined that new and advantageous properties can also be obtained by performing friction stir processing and friction stir mixing (see for example the application having Ser. No. 11/090,910 and filed Mar. 24, 2005). Friction stir processing is a solid state process created by friction that uses a tool not to join materials together in welding, but to instead condition or treat the surface or all of a material by running the tool through at least a portion of the material being processed.
Friction stir mixing is similar to friction stir processing as described above, but combines with it the aspect of mixing in one or more different materials into a base material or workpiece to create a new material having advantageous characteristics as compared to the original base material.
Liquid State Processing of Materials
The periodic table outlines and organizes the elements that are used to engineer all of the materials developed and produced today. Each of these elements can exist in solid, liquid, or gaseous states depending on temperature and pressure. Solid materials created from these elements such as metallic ferrous alloys, metallic nonferrous alloys, metal matrix composites, intermetallics, cermets, cemented carbides, polymers, and others undergo specific processing to create the material's desired physical and mechanical properties.
Each of the previously named solid material types was created by mixing the elements together in some fashion and applying heat and/or pressure so that a liquid and/or liquid-solid mixture is formed. The mixture is then cooled to form the resulting solid material. The solid material formed will have a characteristic microscopic crystalline or granular structure that reveals some of the processing characteristics, phases of element mixtures, grain orientation, etc. For example, mild steel is made by mixing specified amounts of carbon and iron together (along with trace elements) and heating the mixture until a liquid is formed. As the liquid cools and solidifies, steel is formed.
Cooling rates, subsequent heat treatments and mechanical processing will affect the microstructure of the steel and its resulting properties. The microstructure reveals a granular structure having an average specific grain size and shape. Many decades of research and engineering have been dedicated to understanding and creating different materials from a variety of elements using temperature and mechanical processing to create desired material and mechanical properties.
Engineered materials such as metallic ferrous alloys, metallic nonferrous alloys, metal matrix composites, intermetallics, cermets, cemented carbides and others all require a process that melts some or all of the elements together to form a solid. However, there are several problems that occur as a result of having this liquid to solid phase transformation.
For example, during the liquid phase, the time at temperature and/or pressure often becomes a critical variable. Some elements dissolve into submixtures while others precipitate out as they are combined with other elements to form new phases. This dynamic behavior is a complex interaction of elemental solubility, diffusion characteristics, and thermodynamic behavior. Because of these complexities, it is difficult to engineer a material from the beginning. The material is instead developed through trial and error experimentation. Even when a specific elemental composition is determined, the liquid phase processing can have a multitude of process parameters that will alter the resulting solid material's properties. During this liquid phase, time, temperature and pressure play a critical role in determining the material's characteristics. The more elements combined in the mixture, the more difficult liquid phase processing becomes to produce a predictable material.
As the mixture solidifies, undesirable phases precipitate into the solid structure, detrimental dendritic structures can form, grain size gradients are created from temperature gradients, and residual stresses are induced which in turn cause distortions or undesirable characteristics in the resulting material. Solidification defects such as cracking and porosity are constant problems that plague the processing of materials formed from a prior liquid phase. All of these problems combine to lower a given material's mechanical and material properties. Unpredictability in a material's properties results in unpredictability in a component's reliability that is made from such materials.
Because of these solidification problems and resulting defects, additional mechanical and thermal processes are often performed in order to bring back some of the material's desirable properties. These processes include forging, hot rolling, cold rolling, and extrusion to name a few. Unfortunately, mechanical processes often give the material undesired directional properties, reduce ductility, add incremental residual stresses and increase cost. Heat treatments can be used to relieve residual stresses, but even these treatments can cause grains to grow and other distortions to occur.
It is often the case that the bulk size of materials being processed prohibits shorter processing times needed to prevent grain growth. The thermal capacitance of these large bulk materials also maintains elevated temperatures for extended periods of time which by itself also creates an environment for detrimental prolific grain growth. Unfortunately, quickly dropping the temperature of the bulk material through quenching is again problematic because cracking and residual stresses that approach the tensile strength of the material can be formed.
Thus it should be apparent why it is so difficult to design and produce a material with a given grain size, grain size distribution and elemental composition that has a desired range of properties when it is necessary to use a liquid phase mixture to create the solid material.
For example, manufacturers of many materials desire to produce very fine grain (sub-micron) microstructures to obtain the highest possible material and mechanical properties possible. Presently, fine grain microstructures are achieved with the addition of grain growth inhibiting elements or mixtures to the liquid phase of the processing. While reducing grain size, these inhibitors often cause other material processing problems. Some of these problems include lower strength of the material, grain boundary defects, and detrimental phases.
High Temperature Friction Stir Welding Tool
In conjunction with the problems associated with the creation of materials that require liquid to solid phase transformation, recent advancements in friction stir welding technologies has resulted in tools that can be used to join high melting temperature materials such as steel and stainless steel together during the solid state joining processes of friction stir welding.
This technology involves using special friction stir welding tools capable of withstand higher operating temperatures. FIG. 2 shows one example of a friction stir welding tool that can be used in high temperature applications. In this example, the tool comprises a polycrystalline cubic boron nitride (PCBN) tip 30, a locking collar 32, a thermocouple set screw 34 to prevent movement, and a shank 36.
When this tool is used it is effective at friction stir welding of various materials. This tool design is also effective when using a variety of tool tip materials besides PCBN. Other materials that may be used include and PCD (polycrystalline diamond) and refractories such as tungsten, rhenium, iridium, titanium, molybdenum, etc.
Because these tip materials are often expensive to produce, a design having a replaceable tip is an economical way of producing and providing tools to the market because they can be replaced when worn or fractured.
Applications Requiring Durable Higher Melting Temperature Materials
Many applications require the use of durable and/or higher melting temperature materials. These applications include, but are not limited to: oil and gas exploration, development, recovery, transportation, storage and processing; mining; construction; petrochemical; defense; and other industrial applications. For example, in oil and gas exploration and production, products and engineering services that include the use of durably higher melting temperature materials include drilling and completion fluid systems, solids-control equipment, waste-management services, production chemicals, three-cone and fixed cutter drill bits, turbines, drilling tools, under reamers, casing exit and multilateral systems, packers and liner hangers, to name a few.
Products and services in the industries described above typically require equipment and tools that must operate in harsh or demanding environments. While the wearing down or failure of parts and components is an expected reality, tremendous benefits may be obtained if the life of parts and components can be extended and/or their performance or reliability improved. For example, in oil and gas exploration consider a roller cone drill bit connected to the distal end of a drill string to drill a well bore that may span a mile or more in length underground. When a bit component, such as the seals or bearings fail, the entire drill string must be extracted to retrieve and replace the bit. This can result in a significant cost to a drilling operation because of the ancillary equipment, manpower, and time required retrieving and replacing the bit. Thus, a significant benefit can be obtained by providing or using a bit having longer lasting components.
In general, methods and techniques that can be used to produce parts, components, tools, and/or equipment having an increased life-cycle and/or improved performance and/or reliability are greatly desired in these and other applications.
Historically, there have been two main types of drill bits used drilling earth formations, drag bits and roller cone bits. The term “drag bits” refers to those rotary drill bits with no moving elements. Drag bits include those having cutters attached to the bit body, which predominantly cut the formation by a shearing action. Roller cone bits include one or more roller cones rotatably mounted to the bit body. These roller cones have a plurality of cutting elements attached thereto that crush, gouge, and scrape rock at the bottom of a hole being drilled.
Roller cone drill bits typically include a main body with a threaded pin formed on the upper end of the main body for connecting to a drill string, and one or more legs extending from the lower end of the main body. Referring to FIG. 88, a conventional roller cone drill bit, generally designated as 110, consists of bit body 111 forming an upper pin end 112 and a cutter end of roller cones 113 that are supported by legs 114 extending from body 111. Each leg 114 includes a journal 115 extending downwardly and radially inward towards a center line of the bit body 111, with cones 113 mounted thereon. Each of the legs 114 terminate in a shirttail portion 116. The threaded pin end 112 is adapted for assembly onto a drill string (not shown) for drilling oil wells or the like.
Conventional roller cone bits are typically constructed from at least three segments. The segments are often forged pieces having an upper body portion and a lower leg portion. The lower leg portion is machined to form the shirttail section and the journal section. Additionally, lubricant reservoir holes, jet nozzle holes, and ball races are machined into the forgings. Roller cones are rotatably mounted to a bearing system on the formed journals, and the leg segments are positioned together longitudinally with journals and cones directed radially inward to each other. The segments may then be welded together using conventional techniques to form the bit body. Upon being welded together, the internal geometry of each leg section forms a center fluid plenum. The center fluid plenum directs drilling fluid from the drill string, out nozzles to cool and clean the bit and wellbore, etc.
Roller cone bits may use a roller bearing system, a journal bearing system, or a combination of the two to allow rotation of the roller cones about the journal. Each type of bearing system is ordinarily comprised of a number of separate components, including primary bearings, secondary bearings, a seal system, features that resist thrust loading, and a lubrication system. Also typical to both bearing systems are cone retention balls, which are used to prevent roller cones from separating from their journals.
Generally, roller bearing systems use rollers to separate the roller cones from the journal. A cone retention ball bearing is usually provided to carry axial load, and the rollers typically carry radial loads. Journal bearing systems, on the other hand, use a film of lubricant to separate the roller cones from the journal. The inner surfaces of roller cones are specially designed so the film of the lubricant prevents contact between the roller cone and journal. Roller bearings are common in roller cone drill bits, especially in roller cone drill bits with diameters larger than twelve inches, because they can reliably support large loads and generally perform well in the drilling environment. Bits having small diameters commonly use journal bearing systems because there is less space to install suitably sized rollers in a small cone.
Referring to FIG. 89, a typical ball bearing system is shown within a roller cone drill bit leg. Roller bearings 201 are placed around the journal 202 prior to sliding the journal 202 into the roller cone body 203. Alternate bearing systems may be used to separate the roller cone body 203 from the journal 202, such as floating bearings or a journal bearing system. The journal 202 has a journal race surface 204, and the roller cone body 203 has a roller cone race surface 205, which meets to form a ball race 206. A ball hole 207 extends from the back face 208 of the drill bit leg 209 to the journal race surface 204. A plurality of cone retention balls 210 are then inserted through the ball hole 207 into the ball race 206, to hold the roller cone 203 on the journal 202. Once the balls 210 are in place, a ball hole plug 211 is inserted into the ball hole 207 and welded into place, to prevent the roller cone 203 from slipping off the journal 202.
To prevent damage to the cone retention balls 210 and edges of the ball hole 207, cutter designs known in the art have the ball hole 207 placed at 180 degrees from the load bearing zone of the journal 202. This placement is selected to prevent forcing the balls 210 against the rough edges of the ball hole 207 as they pass over the hole 207. If the ball hole 207 were positioned in the load bearing zone, the balls 210 would forcibly impact the edges of the ball hole 207, probably resulting in metal chips and debris being removed from the journal 202 so as to contaminate the lubricant and eventually destroy the bearings and seals.
Contained within the bit body is a grease reservoir system (not shown). A lubricant passage 212 is provided from the reservoir to race surfaces 204, 205 formed between the journal 202 and roller cone body 203, to lubricate race surfaces 204, 205 by a lubricant or grease composition. Lubricant or grease also fills the portion of the ball hole 207. Lubricant or grease is retained in the bearing structure by a resilient seal 213 between the roller cone 203 and journal 207.
For many applications, roller cone drill bits are limited by the bearing capacity or bearing life of the bit. A contributing cause of bearing failure in roller cone systems is failure of the weld joint between the ball hole plug and the back face of the leg. In addition to providing a secure weld, protection of the weld joint from wear, erosion and corrosion is necessary to prevent failure of the plug and/or leg in the plug region, and ultimately, failure of the bit.
Current methods of welding the ball hole plug to the back surface of the bit leg are difficult to implement and may cause flaws in the weld joint. For example, GMAW welding can cause porosity, inclusions, cracks and an area of un-fused material at the weld root, any of which can lead to premature failure by initiating fatigue stresses. Further, in gas or plasma arc welding, heat of the arc weld and molten weld deposit can potentially affect the seal integrity of the weld joint. Additionally, dissimilar chemistry in a deposit weld metal and the leg steel may cause galvanic corrosion in caustic or acidic drilling conditions.
Another cause of bearing failure in roller cone drill bit systems is spalling, which may occur, for example, when the ball hole plug is not exactly in line with the journal race surface and continuously passing retention balls flake off material from the plug. When the surface spalls, debris contaminates the lubricant which causes rapid wear and damage to the rest of the operable bearing and seal components which eventually results in bearing failure. Accordingly, there exists a continuing need for developments in securing a ball hole plug to a bit leg that may at least provide for increased bearing life.